The spatial organization of the cell depends upon intracellular trafficking of cargos along microtubules and actin filaments. The kinesin, dynein, and myosin families of motor proteins transport diverse vesicles and organelles including mitochondria, endosomes, and even viruses that have entered the cell. A great deal of effort has gone into understanding how individual components of this transportation system work, e.g., single molecule studies of motors. However, little is known about how function emerges from multiple interacting components of the transport pathway, especially how multiple motors function both to haul cargos along filaments, and to switch between filaments. The goal of the proposed research is to understand how intracellular transport operates and how it is regulated. In particular we have the following aims: 7 Aim 1: : Determine whether multiple motors on a cargo move and share load cooperatively or independently. 7 Aim 2: Determine the role of switching via a tug of war between the motors on intersecting filaments. 7 Aim 3: Determine whether proteins that bind to filaments regulate switching between filaments. We will interpret the results of quantitative experiments using Monte Carlo simulations. Relevance to public health: The organization inside a cell is maintained through a transportation system in which molecular motors haul cargo from one place to another. The breakdown of this transportation system has been associated with neurodegenerative diseases such as Parkinson's disease and Alzheimers, while disruption of intraflagellar transport can lead to polycystic kidney disease, blindness (retinitis pigmentosum), and developmental defects such as Situs Inversus where organs are misplaced on the wrong side of the body. A better understanding of fundamental intracellular transport processes will aid in the design of new therapeutic approaches.